The sight radius would have no bearing on near far zero, but it does have a direct affect on point of impact adjustments to the front and rear sights pertaining to elevation. The Shorter sight radius equates to more aggressive adjustments on the carbine. An optic eliminates sight radius but the rifle or carbine would have the same near and far zero despite a change from irons to optics.

See the following chart which discusses the more aggressive elevation adjustments going from rifle to carbine:



Remember the M16A2 is a 1 minute drum, where as the M4 and A4 are 1/2 minute from the detachable carry handle.



It should get you on paper. A 25 yard zero has a very far zero at 400 ish yards with m193 according to my ballistic calculator. In my case, striking low could be due to a grouping slightly below the center of mass on the shilouette in addition i did not use sling tension to obtain my 25 yard zero. I proceeded to use sling tension for the 300 yard portion of the shooting on a non free floated barrel. This is why I believe I had to come up on the front sight.

This method works well,  but with all the setups people have out in TV Land YMMV.





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Awesome video. Thanks.

On the carbine you leave it at 8/3 or 6/3 when at 25 yards where as on a rifle you click up one when zeroing then click down to set you bzo. The relationship between sight radius and the angle of the barrel absolutely effect the near far zero.

I believe Molon explaines this much better than that

I get what your saying, and yes the sight radius of iron sights affects the changes in point of impact on the M4s irons as they were developed with the geometry of a 20inch M16. When pressed into the role of a M4 with its shorter site radius the geometric changes lead to more aggressive elevation adjustments. The m16A4 carry handle was not calibrated for the carbine. This has everything to do with how the carbine with its short sight radius relate to the adjustments on the sight which match 1/2 minute elevation adjustments for a 20 inch gun and its sight radius geometry.

Put on a optic and the gun and eliminate sight radius and your near and far zero will be related to muzzle velocity. If you zero a 20 inch gun with its higher muzzle velocity and zero a m4 with its lower velocity both at 25 yards, the far zero will be further for the projectile who's muzzle velocity is highest.